The present invention relates to a method and apparatus for nebulizing a liquid. The invention is particularly applicable for use in producing a stream of heated vapor containing liquid droplets to be used for therapeutic purposes, and is therefore described below with respect to this application.
It has recently been shown that the application of a stream of heated vapor to the nasal passages can have a beneficial therapeutic effect on persons suffering from a common cold and other similar ailments, such as sinusitis, allergic and non-allergic rhinitis, nasal polyps, asthma and hay fever. Several patents, for example U.S. Pat. Nos. 4,369,777 and 4,401,114, have issued describing this treatment, and machines are now commercially available for providing this treatment. However, while the treatment has been found to be very effective, the machines now in use are large and noisy, tend to overheat at the entrance to the nostrils, tend to produce considerable water splash, are frequently unreliable, and are very expensive.
A number of prior patents describe a method of nebulizing a liquid by operating an ultrasonic generator, such as a piezoelectric crystal, while submerged in a pool of a liquid to be nebulized. This produces a spout of intensely-agitated liquid spouting upwardly out of the surface of the liquid pool. Examples of patents describing this technique are Gauthier et al. U.S. Pat. No. 3,387,607, Boucher U.S. Pat. No. 3,5561,444, Weaver et al. U.S. Pat. No. 3,593,712, Mitsui U.S. Pat. No. 3,901,443, Nishikawa et al. U.S. Pat. No. 4,410,139, and German Pat. No. DE 3049244. Mitsui U.S. Pat. No. 3,901,443 is of particular interest since it discloses that mounting the ultrasonic generator at an inclination of 2.sup.0 -22.sup.0 with respect to the surface level of the liquid was found to increase the nebulizing capacity of the device; and Nisikawa et al. U.S. Pat. No. 4,410,139 is also of particular interest since it discloses that providing a partition surrounding the spout in order to separate the larger non-vaporized particles from the spout base reduces the disturbance to the formation of the spout at the spout base.
Various means are also described in the prior patents for protecting the ultrasonic generator should the level of the liquid fall below a predetermined level.
An object of the present invention is to provide an improved method and apparatus for nebulizing a liquid in a manner which substantially increases the nebulizing capacity and also minimizes the disturbance to the formation of the spout by the fall-back of droplets from the spout into the liquid pool.
Another object of the invention is to provide a nebulizing method and apparatus which includes an improved liquid-level detector means for preventing damage to the ultrasonic generator should the level of the liquid fall below a predetermined level.